3. And God said, Let there be light: and there was light.
4. And God saw the light, that it was good: and God divided the light from the darkness.
5. And God called the light Day, and the darkness he called Night. And the evening and the morning were the first day.
This light mentioned above could not have come from the sun because the sun did not yet exist. There are several observations to make about this light. The first is that this light had no source but was created in space by God. This light came from every direction in space as indicated by the need to separate out darkness to make night. This could have been accomplished by use of a dark cloud to block light on one side.
Astronomers have observed this type of light. A light coming from every direction without any observable source, in the form of the Cosmic Background Radiation. (CBR) While this is microwave radiation and not visible light, an expansion factor for the universe of 3300 (from 4.1 million to 13.5 billion Light Years) would convert the visible light to microwaves. This is a much smaller expansion than required by the Big Bang model so it is quit possible.
Note the phrase in verse 5, “The evening and the morning were the first day”. This clearly shows that the days of Creation were normal Earth days.